Field of the Disclosure
The present disclosure relates to processing sapphire using lasers in a wavelength range of about 1060-1070 nm, and more particularly, relates to laser processing sapphire with a modulated single mode (“SM”) fiber laser system operating in a quasi-continuous wave mode (“QCW”).
Background Art Discussion
Hard materials such as sapphire (Al2O3) are used for many industrial applications such as optical windows, hard materials preventing abrasion, and buffer materials for semiconductor emitting device, and the like. Conventional mechanical methods for treating or processing sapphire substrates include diamond scribing and blade dicing. When using these methods, the low depth of the scribe can lead to breaking the substrate, which lowers production yields, for example, when manufacturing of LEDs. Other problems associated with blade dicing include formation of debris (which may require post-cutting cleaning), stress induced into the substrate, and the relatively large width of the cut known as kerf.
Laser processing methods have been used in an effort to increase efficiency because they provide a noncontact process that is more efficient for high volume production. The laser scribed cutting depth may also be controlled to reduce stress on the wafer during the break process. Also, laser scribing facilitates precise positioning of scribes within a few microns of active features along with a narrow scribe width with fewer chippings. Thus, laser processing has overall advantages of increased throughput, low cost, ease of use, and high yields compared to traditional mechanical methods.
Certain materials, however, present challenges when processing using lasers. The bandgap of sapphire, for example, is approximately 8 eV, and under normal low intensity illumination, sapphire is optically transparent from 5000 nm to about 300 nm. Therefore, conventional laser processing of sapphire has used lasers that are more likely to be absorbed in sapphire, such as DUV and UV lasers operating in a wavelength range between about 157 and about 355 nm.
One technique for laser processing of sapphire involves ablation, which is a vaporization of the material resulting from a combination of bulk heating of the material and avalanche ionization. Ultrafast lasers (e.g., picosecond and shorter pulse widths) and/or Q-switched pulse lasers with nanosecond pulse widths may be used to emit pulses with high peak power capable of ablating sapphire. The high intensity drives a nonlinear, multiphoton absorption process which excites electrons in the material and directly breaks bonds. However, high peak power may thermally damage the cut edge because the heat from the absorption of the laser beam has time to diffuse into the substrate.
Another laser processing technique involves scribing and breaking along internal modification regions inside the sapphire. The output of a picoseconds laser, for example, may be focused inside the sapphire substrate creating cracks within the substrate without affecting the top and bottom surfaces. Once these cracks are produced, the individual pieces may be broken out from the substrate using mechanical means such as tape expansion. This two-step process, however, may be time consuming and cost inefficient.
A further technique for laser processing materials with a low absorption coefficient includes water jet laser processing. Water jet laser processing involves focusing a laser beam into a hair-thin, low-pressure water jet, which then guides the laser beam onto the wafer. Water jet laser processing systems, such as the Laser-Microjet® system, may prevent heat damage and contamination but also involves a more complex and expensive system. A Q-switched Nd:YAG laser operating at 1064 nm and frequency-doubled Nd:YAG lasers operating at 532 nm are particularly adapted to the water jet-guided cutting technology.
The existing techniques used for laser processing of sapphire discussed above suffer from some of the same drawbacks. In particular, the cost of pulsed lasers is high. Also, the wavelengths used in UV cutting require the use of crystals, which may have a short useful life and may present issues with the maintenance of these lasers. Although excimer lasers may be used, these lasers generally have large dimensions and low efficiency.
Accordingly, a need exists for a system and method of laser cutting sapphire substrates at wavelengths of around 1060-1070 nm with reduced cutting edge defects and increased speeds in a time-effective and a cost-effective manner.